Ballasting device



C. J. DAVISSON.

BALLASTING DEVICE.

APPLICATION FILED DEC.23, 1919.

1,364,080. Y Patented Jan. 4, 1921.

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. M van for C///770/7 JfldV/JJW? yW K M UNITED STATES PATENT OFFICE.

I. CLINTON ,J' DAVISSON, OF MAPLEWOOD, NEW JERSEY, ASSIG-NOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF. NEW YORK, N. Y., A CORPORA- TION OF NEW YORK.

BALLASTING DEVICE.

Patented Jan. 4,1921.

Application filed December 23, 1919. Serial No. 347,031.

T 0 all whom it may concern.

Be it known that I, CLINTON J. D AVISSON, a citizen. of the United States, residing at -Ma-plewood, in the county of Essex and State of New Jersey, have invented certain new and useful Improvements in Ballasting Devices, of which the following is a full, clear, concise, and exact description.

This invention relates to an improvement in the construction of regulating devices for electrical circuits, the purpose of such devices being to steady an otherwise fluctuating current. It relates to that class of devices which employs a resistance element having a positive temperature coefficient,

- that is one whose electrical resistance increases with its temperature.

The so-called ballast. lamp belongs to the classification referred to above. It has been employed as a steadying means in connection with Nernst glower circuits, mercury arc lamps and telephone repeater circuits.

The usual construction of such a ballasting device has consisted in a coil of suitable resistance wire, such as chemically pure iron wire, mounted within a glass bulb which has been either evacuated or filled with an inert as. The objections to such constructions of this kind are the excessive cost of manufacture and the comparatively large amount of space which they occupy. I

The object of this invention is to provide a satisfactory current regulator which will be simple and inexpensive to construct and one which can be confined in a minimum of space.

While the present invention may be employed as a regulator in many types of electrical circuits, its use in connection with telephone repeater circuits will be more particularly referred to in this specification.

In constructing a ballast device the first prerequisite of course is that the ratio of the power consumption in the resistance element to the resistance of the wire or other material used, shall be constant over a considerable range of power. If this condition be satisfied it necessarily follows that the current passing through will be uniform over the corresponding voltage range. Now

both the power consumption and resistance values are functions of the temperature of the reslstance element. This may be expressed,

- fi 1 o) f2( 1 0) where Pzpower consumption, Rzresistance of the resistance element, and t et z lncrement of temperature.

The desired condition then is:

values, R (t t) where a is a constant.

Obvously, then, in order to satisfy the relation as shown by (1), it is necessary where B is a constant. 7

It hasbeen found that this may be accomplished when the heat energy dissipation from the resistance element is controlled by selecting a proper'medium by which said resistance element may be surrounded.

Resistance elements embedded in glass, or the like, so that the heat developed therein may be transferred uniformly to the atmosphere or other heat absorbing medium, by conduction, have proven to be well suited in satisfying the conditions set forth above.

Referring now to the drawings, which will enable one skilled in the art to understand more readily the application and preferred'form of the invention, Figures 1, 2, and 3 illustrate three different embodiments of the invention. q

Fig. 1 shows one form of the device in the and circuit with a mechanical telephone repeater, 1. The resistance wire 2, which in this case is chemically pure iron wire, is welded at its ends to the wires 3, 3, which are made from a metal of good electrical conductivity, such as, for example, copper. While it has been found that the iron wire mentioned above is well suited for the carrying out of the invention, any wire composed of a metal or alloy whose resistance is approximately proportional to the increment in tempera ture when expressed in centigrade units, may be used. The wire is sealed in a suitable sealing medium 4:. There are certain characteristics which this sealing medium must possess. I

1st. It must be capable of adhering to the resistance element employed.

2nd. It must protect the wire from atmospheric action.

3rd. It must be a non-conductor of electricity.

4th. It must be non-inflammable.

5th. It must be capable of contracting and expanding Without becoming disrupted.

6th. It must be able to conduct the heat from the wire to such a degree that the requirements as set forth above may be satistied.

Glass which is capable of withstanding large changes of temperature has been found well suited for this purpose.

Although glass is ordinarily considered as a non-conductor of heat, it will serve as a medium for transferring heat under certain circumstances. Take for example, the application of glass utensils in the laboratory and the home. The materials to be heated or cooked are placed in the utensil and heat applied thereto. The heat passes through the glass walls of the vessel and becomes absorbed by the material therein. It is true, however, that the point of application of the heat must not be removed any great distance from the heat absorbing body. If this were the condition, the conduction of the heat would be very poor.

In carrying out this invention, moreover, it is necessary to provide a sheath for the wire which will allow the heat to be dissipated uniformly. That is to say, the distance from the wire through the sealing medium to the heat-absorbing material, which is the atmosphere, should be uniform for any two relative surfaces of the wire and medium. Hence the covering will take a cylindrical form; its thickness depending upon the degree of conduction desired.

Another advantage derived from the use of glass lies in the fact that on account of the way in which glass is ma de, the chemical and physical properties of any one part of the sheath are identical with those of any other part. This will tend to promote an even distribution of the heat over the wire,

and prevent any deviation in eiiiciency of the device on that account.

In some cases it has been found more desirable to modify the construction as is disclosed by Fig. 2 of the drawings. This differs from that shown in Fig. 1 in that an other material such as alundum cement, kieselguhr, asbestos and the like, is employed in addition to the embedding medium. The wire 2 welded at its ends to the leading-in wires 3, 3, is shown embedded in the glass coating l. A heat-insulating material 5, such as above mentioned, held in position by a containing tube 6, and end plugs 7 7, surrounds that part of the glass in which the resistance element is embedded. Such a heat insulating covering while being required in certain cases to prevent damage from the heat evolved, does not interfere with the operation of the ballasting device.

In case a long length of the iron wire is required in order to give the necessary resistance for use in any particular circuit the wire may be reflexed or coiled, and sealed in the glass in this manner. Fig. 3 of the drawings represents the form of the device-when the wire is coiled.

The .above constructions are the preferred embodiments of the invention. It is evident, however, that the invention may find'expression in a great variety of forms.

\Vhat is claimed is:

1. An electrical ballasting device, comprising a positive temperature coeilicient resistance element, embedded in an electrical insulating, heat conducting medium, the axis of said resistance element being congruent with that of the external surface of said medium.

2. An electrical ballasting device, comprising a positive temperature coefficient resistance element, embedded in glass, the axis of the resistance element being congruent with that of the external surface of said glass.

3. An electrical ballasting device, comprising a positive temperature coefiicient resistance element consisting of chemically pure iron wire, embedded in an electrical insulating heat conducting medium, the axis of said resistance element being congruent with that of the external surface of said medium.

l. An electrical ballastingdevice, comprising a positive temperature coeiiicient re sistance element, consisting of chemically pure iron wire, embedded in glass, the axis of said resistance element being congruent with that of the external surface of said glass.

5. An electrical ballasting device, comprising a positive temperature coetlicient resistance element, embedded in an electrical insulating, heat conducting medium, the axis of said resistance element being congruent with that of the external surface of said with that of the external surface of said medium, and a covering of refractory, heatglass and a covering of refractory heat-in- 10 insulating material surrounding same. sulating material surrounding same.

6. An electrical ballasting device, com- In witness whereof I hereunto subscribe prising a positive temperature coefiicient remy name this 19th day of December, A. D. sistance element, consisting of chemically 1919. pure iron Wire, embedded in glass, the axis of said resistance element being congruent CLINTON J. DAVISSON. 

